This invention relates to the polymerization of conjugated diene monomers using a catalyst system containing a compound of a rare earth element, i.e. an element having an atomic number of 57 to 71 inclusive.
Use of lanthanide series catalysts in the synthesis of 1,4-trans-polybutadiene is known in the prior art. For instance U.S. Pat. No. 4,619,982 to Jenkins, discloses the use of various catalyst systems containing rare earth compounds for the polymerization of conjugated diene monomers, in recent years. Examples of such disclosures are (1) Mazzei A., Makromol. Chem. Suppl. 4 61 (1981); (2) Witte J., Angew. Makromol. Chem. 94 119 (1981); (3) Shen Tse-Chuan et al, J. Pol. Sci. Polym. Chem. Ed. 18 3345 (1980); (4) Marwede G. and Sylvester G., Trans. 22nd Annual Proceedings of the International Institute of Synthetic Rubber Producers, Madrid Paper III-3 (1981). Such catalyst systems have two or three components, for example a lanthanoid alkyl, alkoxide or salt (e.g. neodymium tricarboxylate) with an organoaluminium compound and optionally a Lewis Acid. When a -allyl complex of a rare earth such as Ln(allyl) dioxane, where Ln also a lanthanide element, is used which gives a polymer of predominantly trans 1,4 content, and which needs no cocatalyst. Such -allyl catalysts are described in the paper by Mazzei referred to above and appear to proceed by an ionic mechanism.
One embodiment of the Jenkins invention discloses a two component catalyst for the homo polymerization of a conjugated diene or the copolymerization of a conjugated diene with one or more other conjugated dienes comprising (a) a salt of a rare earth element or a complex of a rare earth element and (b) an organo magnesium compound. The Jenkins invention also includes the use of a catalyst, as just defined, in the homo polymerization of a conjugated diene. Surprisingly, Jenkins found that the product of such a polymerization employing an organo magnesium compound as cocatalyst is a conjugated diene polymer having a very high content of trans isomer. The rare earth element in component (a) of the catalyst of are those having an atomic number of 57 (lanthanum) to 71 (lutetium). However, the polymerization activity of certain of these elements, e.g. samarium or europium, is known to be low. Thus, a compound of cerium, praseodymium, neodymium, gadolinium, terbium or dysprosium is preferred by Jenkins. A compound of two or more rare earth elements may be used. A compound of neodymium or "didymium" (which is a mixture of rare earth elements containing approximately 72% neodymium, 20% lanthanum and 8% praseodymium) is preferred. Preferably component (a) is soluble in hydrocarbon polymerization medium, examples being the carboxylates, alkoxides and diketones. Examples of compounds for use as component (a) are "didymium" versatate (derived from versatic acid, a synthetic acid composed of a mixture of highly branched isomers of C.sub.10 monocarboxylic acids, sold by Shell Chemicals), praseodymium (2,2,6,6-tetramethyl-3,5-heptane dione). "Didymium" and especially neodymium "versatate" are preferred on the grounds of ready solubility, ease of preparation and stability. Component (b) of the catalyst is an organo magnesium compound. Dihydrocarbyl magnesium compounds of formula R.sub.2 Mg where each R, which may be the same or different, is for example, an alkyl (including cycloalkyl), aryl, aralkyl, allyl or cyclodiene group. Dialkyl magnesium compounds, where each alkyl group has from 1 to 10 carbon atoms, are preferred. Magnesium dibutyl was particularly preferred by Jenkins on the grounds of ease of availability. The organo magnesium compound may also be a hydrocarbon soluble Grignard reagent of formula RMgX where R is a hydro-carbyl group such as exemplified above and X is chlorine, bromine or iodine. The molar ratio of component (a) to component (b) was preferably 0.01:1 to 0.5:1 more preferably 0.06:1 to 0.3:1. Absolute concentration of component (b) may be for example, 1 to 5 millimoles per hundred grams of polymerisable monomer. Similarly in the publication Polymer, 1985, 26, p147, D. K. Jenkins disclosed experiments wherein high trans polybutadiene was obtained by using a catalyst system comprising a rare earth compound plus a magnesium dialkyl. The polymer appeared to contain some "live" chain ends.
In another U.S. Pat. No. 4,931,376, to Ikematsu et al, another process for the homopolymerization of a high-trans polybutadiene is described. Ikematsu provides a process for producing crystalline trans-butadiene polymers. The process comprises: using a complexed catalyst comprising (a) an organic acid salt of lanthanum or cerium and (b) an organic magnesium compound as the essential components. Lanthanum and cerium which are the main components in the complexed catalyst of the Ikematsu invention are metals occurring abundantly among lanthanide transition metals (rare earth metals) and commercially readily available at relatively low cost. Ikematsu unexpectedly found that a conjugated diene can be polymerized by using the complexed catalyst of the present invention to provide a conjugated diene polymer having high trans content at a very high activity, and yet the polymer obtained has a high molecular weight and a narrow molecular weight distribution, containing substantially no gel, the polymer thus obtained exhibiting excellent workability and physical properties. The organic acid salt of lanthanum or cerium which is the component (a) in the complexed catalyst of the present invention can readily be obtained by, for example, making an alkali metal salt of an organic acid as shown below to react with a chloride of lanthanum or cerium in water or an organic solvent such as alcohols, ketones, etc. The organic acid salt of lanthanum or cerium may contain inorganic salts of lanthanum or cerium or organic acids as the impurities in small amounts.
Various lanthanide series catalysts are known by the prior art. For instance, see: J. Am. Chem. Soc., vol. 104, pp. 6571-6473 (1982), Patricia L. Watson and D. Christopher Roe, "Beta-Alkyl Transfer in a Lanthanide Model for Chain Termination;" J. Am. Chem. Soc., vol. 107, pp. 8091-8103 (1985), Gerald Jeske, Harald Lauke, Heiko Mauermann, Paul N. Swepston, Herbert Schumann and Tobin J. Marks, "Highly Reactive Organolanthanides. Systematic Routes to and Olefin Chemistry of Early and Late Bis(pentamethylcyclopentadienyl) 4f Hydrocarbyl and Hydride Complexes." Also exemplary in displaying the utility of lanthanide series compounds in catalyst systems for the production synthetic rubbers is U.S. Pat. No. 4,152,295 teaching the reaction of a conjugated diolefin with at least one compound selected from the group consisting of a carboxylic acid and a carboxylic acid anhydride in the presence of oxygen and a catalyst comprising a rare earth metal compound, an alkali metal compound and a halide compound.
U.S. Pat. No. 4,461,883 teaches a process for producing a conjugated diene polymer, characterized by polymerizing at least one conjugated diene with a catalyst consisting of: (A) a reaction product of a Lewis base and a carboxylate of a rare earth element of the lanthanum series represented by Ln(R.sub.1 CO.sub.2).sub.3 wherein Ln is a rare earth element of the lanthanum series having an atomic number of 57 to 71 and R1 is a hydrocarbon substituent having 1 to 20 carbon atoms; (B) an organic aluminum compound represented by AlR.sup.2 R.sup.3 R.sup.4 wherein R.sup.2, R.sup.3 and R.sup.4, which may be identical or different, represent hydrogen atoms or hydrocarbon substituents having 1 to 8 carbon atoms, excluding the case where all of R.sup.2, R.sup.3 and R.sup.4 are hydrogen atoms at the same time; and, (C) an (alkyl)aluminum halide represented by AlX.sub.n R.sup.5.sub.3--n wherein X is Cl, Br, F or I; R.sup.5 is a hydrocarbon substituent having 1 to 8 carbon atoms; and n has a value of 1, 1.5, 2 or 3, or consisting of these (A), (B) and (C) components and (D) a conjugated diene. A polymer obtained by the process has a high cis-1,4-configuration content and is excellent in physical properties of vulcanizate.
U.S. Pat. No. 5,612,427 teaches a supported solid catalyst which can be used for the polymerization and copolymerization of conjugated dienes. The basis of the catalyst is the reaction product of: A) a solid MgCl.sub.2 support; B) an ether, preferably THF, as swelling agent for the support; C) a metal salt selected from among metals having an atomic number of between 57 and 71 or 92 in the periodic table of elements and, if the metal salt is not a halide; D) a halogenation agent selected from the group consisting of a halogenated compound of aluminum and a halogenated compound not containing aluminum, the reaction solid being free from the swelling agent; plus, E) an organic derivative of aluminum which is obligatory when the halogenation agent is not a halogenated compound of aluminum and optional when the halogenation agent is a derivative of aluminum.
U.S. Pat. No. 4,696,984 teaches isoprene polymers and copolymers which are prepared by a polymerization process carried out in the absence of solvents and in the presence of a catalytic system comprising (a) at least one element or compound of an element pertaining to Group IIIB of the Periodic Table, (b) at least one aluminum alkyl derivative, (C) at least one organic halogen derivative or at least one halide of an element able to exist in at least two valency states with the halide corresponding to a higher state than the minimum, or at least one halogen or at least one hydrogen halide acid, (d) at least one compound containing one or more hydroxyl groups of which the hydrogen can be substituted, the ratio of component (b) to component (a) being equal to or less than 20.
U.S. Pat. No. 5,610,114 teaches a supported solid catalyst which can be used for the polymerization and copolymerization of conjugated dienes. The basis of the catalyst is the reaction product of: A) a solid MgCl.sub.2 support; B) an ether, preferably THF, as swelling agent for the support; C) a metal salt selected from among metals having an atomic number of between 57 and 71 or 92 in the periodic table of elements and, if the metal salt is not a halide; D) a halogenation agent selected from the group consisting of a halogenated compound of aluminum and a halogenated compound not containing aluminum, the reaction solid being free from the swelling agent; plus, E) an organic derivative of aluminum which is obligatory when the halogenation agent is not a halogenated compound of aluminum and optional when the halogenation agent is a derivative of aluminum.
U.S. Pat. No. 5,567,784 teaches the production of diene rubbers polymerized by means of Nd catalysts. The rubbers have a reduced cold flow and a low intrinsic odor. The process is effected by the polymerization of diolefines adiabatically at temperatures of -20.degree. to 150.degree. C., in the presence of inert organic solvents and in the presence of metallo-organic mixed catalysts based on neodymium carboxylate. The reaction mixture obtained in this manner is depressurized, and thereafter treated with disulphur dichloride, sulphur dichloride and/or thionyl chloride sufficient to impart the desired properties.
U.S. Pat. No. 4,990,573 teaches the processability of a polybutadiene with a high content of 1,4-cis-structure which is improved by means of the addition of PCl.sub.3 before the polymerization reaction is quenched and when Mooney viscosity of polybutadiene has reached a prefixed value, preferably lower than, or equal to 30; the polymerization of butadiene is carried out in a solution in an aliphatic or cycloaliphatic solvent, in the presence of a catalytic system based on rare earths, preferably a neodymium-based catalytic system.
U.S. Pat. No. 4,429,089 teaches a method for the polymerization or copolymerization of butadiene or isoprene conducted in the presence of a catalytic system composed of: (A) an aluminum trialkyl having the formula, AlR.sub.3 ; wherein R is an alkyl radical containing from 1 to 20 carbon atoms, (B) an aluminum halide or alkyl aluminum halide having the formula AlX.sub.a R.sub.3-a ; wherein R is an alkyl radical containing from 1 to 20 carbon atoms, X is chlorine or bromine and a is an integer from 1 to 3, and (C) Neodymium alcoholate having the formula, Nd(OR).sub.3 ; wherein R is an alkyl radical containing from 1 to 20 carbon atoms. In one embodiment, the present invention comprises a two component catalyst for the homo polymerization of a conjugated diene while providing the option of a block polymerization of a conjugated diene with one or more other conjugated dienes. The two component catalyst or the invention comprises (a) a salt of a rare earth element or a complex of a rare earth element and (b) an organo magnesium compound. The invention also includes the use of a catalyst, as just defined, in the homo polymerization of a conjugated diene or the block polymerization of a conjugated diene with one or more other conjugated dienes. Surprisingly the product of such a polymerization employing an organo magnesium compound as cocatalyst is a conjugated diene polymer having a very high content of trans isomer. The present invention contrasts with the two or three component rare-earth-containing prior art systems, referred to above, which use an organo aluminum compound as cocatalyst and which, as already mentioned, yield a product having a high content of cis isomer.
However, none of the prior art catalyst systems combines all of the advantages of: requiring only two component catalyst system which requires relatively less costly components to vary the microstructure of the polymer product, while nonetheless providing the option of diblock synthesis. Thus, a long felt need has hitherto existed for such a catalyst system.